To afford occupant protection in motor vehicles it is a common practice to provide air bags which are quickly inflated,when a crash is sensed by an accelerometer and associated controller. Such controllers are able to measure the severity of the crash and the velocity change by analyzing the acceleration so that the airbag inflation is optimally timed. Typically the airbag is deployed by firing a pyrotechnic device which releases or produces gas for inflation at a fixed rate, so that deployment is the same for every type of crash, except for the timing. Further improvement in the deployment can be made by controlling the rate of deployment over time. One way of accomplishing this is by multilevel inflation or variable level inflation.
It has been proposed to include two or more inflators in an airbag and to inflate the airbag in stages by triggering inflators in succession. An optimum control for each inflation is desired.